feat: command layer implementation for AddZitadelProvider (#12020)

# Which Problems Are Solved

This PR contains the command-layer implementation to add an instance IDP
of the type `ZitadelProvider`

# How the Problems Are Solved
- Implementing `AddZitadelProvider` in AdminService 
- Adding the command-layer to create a `ZitadelProvider` and push
`ZitadelIDPAddedEvent`

# Additional Changes
N/A

# Additional Context
- Related to https://github.com/zitadel/zitadel/issues/11823
- Follow-up for PR https://github.com/zitadel/zitadel/pull/12018

---------

Co-authored-by: Copilot <[email protected]>

internal/command/instance_idp_model.go

@@ -1034,3 +1034,43 @@ func (wm *InstanceIDPRemoveWriteModel) Query() *eventstore.SearchQueryBuilder {
 		EventData(map[string]interface{}{"idpConfigId": wm.ID}).
 		Builder()
 }
+
+type InstanceZitadelIDPWriteModel struct {
+	ZitadelIDPWriteModel
+}
+
+func NewInstanceZitadelIDPWriteModel(instanceID, id string) *InstanceZitadelIDPWriteModel {
+	return &InstanceZitadelIDPWriteModel{
+		ZitadelIDPWriteModel: ZitadelIDPWriteModel{
+			WriteModel: eventstore.WriteModel{
+				AggregateID:   instanceID,
+				ResourceOwner: instanceID,
+			},
+			ID: id,
+		},
+	}
+}
+
+func (wm *InstanceZitadelIDPWriteModel) AppendEvents(events ...eventstore.Event) {
+	for _, event := range events {
+		switch e := event.(type) {
+		case *instance.ZitadelIDPAddedEvent:
+			wm.ZitadelIDPWriteModel.AppendEvents(&e.ZitadelIDPAddedEvent)
+		default:
+			wm.ZitadelIDPWriteModel.AppendEvents(e)
+		}
+	}
+}
+
+func (wm *InstanceZitadelIDPWriteModel) Query() *eventstore.SearchQueryBuilder {
+	return eventstore.NewSearchQueryBuilder(eventstore.ColumnsEvent).
+		ResourceOwner(wm.ResourceOwner).
+		AddQuery().
+		AggregateTypes(instance.AggregateType).
+		AggregateIDs(wm.AggregateID).
+		EventTypes(
+			instance.ZitadelIDPAddedEventType,
+		).
+		EventData(map[string]interface{}{"id": wm.ID}).
+		Builder()
+}